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The Boobies are large seabirds found around the globe, primarily in warm waters. My sulid experience is with the truly tropical boobies in the genus
Sula
. In 1989 I spent four months at sea on a NOAA research cruise in the eastern tropical Pacific. The world's foremost tropical seabirder, Bob Pitman (and my "boss" although he was on another boat working in tandem with us), told me to particularly watch for variation in "Masked" Boobies -- he believed there were two species involved: the orange-billed
Nazca Booby
and the yellow-billed
Masked Booby
(at upper left is Pitman's great photo of the two side-by-side on Clipperton I., one of the few places where assortative nesting occurs). Bob's research led to the major publication that split these two taxa (Pitman & Jehl 1998). I took notes & photos on my cruise and then intensive museum & literature research thereafter, leading to my identification paper on these two species (Roberson 1998). In Bob's photo (above left) you can compare not only the differences in bill color, but in bill shape and tail pattern. The Nazca Booby has a reddish-pink to orange bill as an adult, and also often has white central rectrices (Masked Booby is always yellow-billed and black-tailed). Nazca Booby is endemic to islands on the Nazca tectonic plate (primarily the Galapagos) while the Masked Booby nests on tropical islands around the world.

The challenge I particularly undertook in my research was attempting to present criteria for the identification of boobies of this type in juvenal or subadult plumages. Boobies do not begin molt for the first 6-8 months of life. The booby shown at right is in juvenal plumage -- no primary molt has begin -- and in his chocolate-brown dress looks superficially like an adult Brown Booby
S. leucogaster.
It is, in fact, a
juvenal Nazca Booby
. Note it already has a yellow eye (Brown Boobies are dark-eyed). It lacks the broad white cervical collar which is characteristic of most juvenal Masked Boobies, and this individual is already changing bill color. Both species start out with gray bills and both species eventually become yellow at the tip (see the top photo) so the important area is at the base of the bill. In Masked Booby this area gradually changes from gray to greenish-yellow to bright yellow; in Nazca Booby the base of the bill changes from gray to dusty-rose to pinkish-orange to bright orange or reddish-pink. The pale "dusty-rose" or lavender color of Nazca Booby can be seen in this shot (and presents an opportunity for you to determine whether your monitor has good color quality... ahem). [Additional discussion of juvenal Masked v. Nazca Booby identification is on line
HERE
with special reference to a bird on Monterey Bay in Feb 1999].

Boobies are strictly marine birds, feeding primarily on fish, and they come ashore only to nest or roost. The three closely-related gannets (genus
Morus
) breed and summer well beyond the tropics, but I have spent little time in eastern North America, or southern Australia & New Zealand, or South Africa, where gannets are common. [There was a gannet in the north Pacific until the late Pleistocene, but I'm not quite that old.] In the tropics, the most pelagic of all boobies is the
Red-footed Booby
(three next photos, below). They come in a bewildering area of plumages, including both white morph and dark morph adults (upper two shots below).
Immature birds, like the young
Red-footed Booby perched on a dead Ridley's Sea-Turtle
far offshore (left), is also extremely variable in pattern. Indeed, separating imm. Red-foots from imm. Brown Booby can be extremely difficult. The literature is devoid of information about the full range of variation, and I consider it one of the least appreciated field problems in North America today (even rarity committees rely on mistaken assumptions).

Identification topics aside, Red-foots are really cool birds because they rely heavily on flying fish to survive. Often at sea, days away from any land, we would have a cadre of Red-foots circling the ship, waiting for us to flush a flying-fish into flight (below). They would then dash after the glider, trying to snatch it before it resubmerged. Fun for all!

Not only is the identification of boobies a fascinating topic, but boobies can present exceptional panoramas of abundant bird life. Examples include
nesting islands full of Masked Boobies
(below, upper photo of Clipperton Island by Robert L. Pitman; a few scattered Brown Boobies are also present) or the
flights of foraging Peruvian Boobies
(below, lower photo) off the coast of Peru (along with a few Guanay Cormorants
Phalacrocorax bougainvillii
).

Yet another fun aspect of boobies is their vagrancy to California. Four species (five species if my theories about Nazca Booby are correct) have reached the state; indeed, all four (or five) have reached Monterey County, my home. My first experiences in California were with
Blue-footed Boobies
(next two photos). Blue-foots appear in erratic, unpredictable "invasions" which often begin at the Salton Sea [That's me at 19 years of age, with Jolee DeLew, at Salton City -- we'd driven all night and most of the next day to reach here, along with Wally Sumner, in my little red VW bug -- on my first really long "chase" trip in 1971.] There have not been such wonderful invasions in the last 20 years; a good summary on those earlier events are in McCaskie (1970).
Another huge invasion occurred five years later in 1976, and one
Blue-foot
wandered all the way up the Sierran foothills to New Hogan Reservoir, Calaveras County (the photo left is of that bird and me). This lost bird appeared 15 September 1976 and stayed a month; it was found dead in mid-October (Elliott 1976). For many years this was single species for Calaveras County (having failed to write down any common species that day)... a rather fine trivia question.

As a family, the various boobies are closely related. The name "booby" comes from a British seaman's slang for "stupid;" on nesting island the first sailors could walk right up to the birds and hit them over the head. [Indeed, keeping breeding islands free of people and introduced predators is a key to successful nesting in boobies.] Most of the species nest on the ground, as the Clipperton I. shot above shows, but the Red-footed Booby and Abbott's Booby
Sula abbotti
on Christmas Island in the Indian Ocean nest primarily in short bushes and trees. Birds do not breed until they are 2-6 years old, depending on the species. Boobies lack a brood patch (it would interfere with aerodynamics in flight) but, instead, have highly vascularized feet. Although birds on nesting islands seem to be sitting on their eggs during incubation (as do other types of birds), they are, in fact, warming them with the webs of their feet! A nice summary of booby biology is in Carboneras (1992).

At 1012 pages, this is the thickest book I own! It was an attempt to set out, in leisurely detail, everything that was then-known about the boobies of the world. It is totally unlike any other family book -- it is intended to be and is a major research tool. Every species has a complete account of every nesting island, with long dissertations of breeding biology and ecology, and extensive details on behaviors (esp. breeding displays). A few color plates (photos) and many black-and-white photos are scattered throughout. It is an indispensable book for those studying this family.
And yet it is strangely unfulfilling. Although the plumage and soft part details are lengthy, there is no real attempt to get at questions of field identification. It does very little good to have a long list of bill or foot colors from the various populations around the world unless those details are tied down to specifics: at what age and in what population are the feet yellow versus green, etc., etc. Nelson seems to regurgitate everything that anyone has ever said about boobies without trying to sift the wheat from the chaff. In doing so, he overlooks those details that Pitman & Jehl (1998) would later use to show that the "Masked" Boobies on the Galapagos are a different species. The photos in Nelson's own book sometimes show important and definitive characters that are overlooked in the text (such as the lack of cervical collars on Galapagos juvenal boobies). And despite the huge length, there really is not nearly enough about the breeding phenology of each individual island population, details which could lead to new understanding of vagrancy. And their are no color plates aimed at side-by-side identification of species.
In its own way it is a wonderful book, and yet so much is lacking... one must turn to something like Carboneras (1992) for a field guide approach to the worldwide boobies (and then that text is rather weak on inter island populations, and totally overlooks the orange-billed boobies on the Galapagos).

Roberson, D. 1998. Sulids Unmasked: which large booby reaches California. Field Notes 52: 276-287.
(I wanted to call this "Boobies unmasked: the story of big boobies on California beaches" -- but the editors nixed that idea.)